America's long-term deficit problems can be solved by going back to a ratio of government spending to tax revenue that had worked for decades, Blackstone Group CEO Steve Schwarzman told CNBC.

The easiest way for President Barack Obama and Republicans to reach a "fiscal cliff" deal would be for spending to revert to 20 percent of the nation's gross domestic product, with taxes at 18 percent, he said on CNBC's "Squawk Box" Wednesday.

"We're [currently] spending 25 percent of GDP and we're taking in 15.5 percent in tax revenue," he said. "If the two groups are prepared to go back to square one ... there would be plenty of common ground to make a deal," he said.

Schwarzman, who supported Mitt Romney in the last presidential election, acknowledged there are a lot of different prescriptions on how to resolve the fiscal cliff, but said he believes the president is "reaching out aggressively" to Republicans to try to get a deal done.